In enzymology, a methanol-5-hydroxybenzimidazolylcobamide Co-methyltransferase (EC 2.1.1.90) is an enzyme that catalyzes the chemical reaction

methanol + 5-hydroxybenzimidazolylcobamide ${\displaystyle \rightleftharpoons }$ Co-methyl-Co-5-hydroxybenzimidazolylcob(I)amide + H₂O

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Thus, the two substrates of this enzyme are methanol and 5-hydroxybenzimidazolylcobamide, whereas its two products are Co-methyl-Co-5-hydroxybenzimidazolylcob(I)amide and H₂O.

This enzyme belongs to the family of transferases, specifically those transferring one-carbon group methyltransferases. The systematic name of this enzyme class is methanol:5-hydroxybenzimidazolylcobamide Co-methyltransferase. Other names in common use include methanol cobalamin methyltransferase, methanol:5-hydroxybenzimidazolylcobamide methyltransferase, and MT 1.

As of late 2007, only one structure has been solved for this class of enzymes, with the PDB accession code 2I2X.